The present invention relates to hot water supply systems and, more particularly, to a versatile hot water supply system incorporating a vapor generator and feedback control means.
The prior art generally recognizes boilers as the traditional means for supplying heat energy in many applications despite the fact that they may not be easily matchable to the temperature, pressure, and flow requirements of a particular application. One difficulty in this regard flows from the fact that in a boiler these parameters are not independent, and changes in heat throughput at constant flow, for example, are accompanied by changes in temperature, pressure, or both. In addition, conventional boilers are expensive and complex, and require extensive maintenance. In most instances the boiler feedwater requires chemical treatment to retard corrosive wear of the boiler.
Hot water systems of conventional design generally incorporate a feedwater boiler where large amounts of cold water are stored and heated to a selected temperature which depends upon demand requirements. Applications include industrial hot water feed lines, schools and office buildings and commercial hot water markets such as car washes and airports. Water demand generally fluctuates in those instances and much energy can be lost from heating large boilers during time of inactivity. Commercial hot water markets may also include construction sites in locations often not accessible to utility lines. This presents the obvious problem of how to heat the water.
Various prior art embodiments have addressed the need for versatile hot water supply systems which meet the needs of intermediate flow demands and remote utilization. Certain prior art systems have incorporated "in-line", electrical heating elements which directly engage the high pressure water flow along a select flow path for heating the water to a select temperature as it passes through the heater. Problems of cost, fuel energy conservation and limited demand capacity have been found to be prevalent in such systems.
Commercial hot water systems must overcome numerous obstacles, yet the potential applications are plentiful. High pressure flooding of hot water in petroleum reservoirs is a proven technique. Equally feasible, both economically and logistically, is vaporization of LPG or propane for combustion. Similarly, line heating of natural gas and/or heavy oil pipelines to promote flow or to avoid condensation therein is a present need. Such commercial/industrial applications which are remotely disposed from power utility systems present a myriad of technological problems for maximally efficient hot water systems. Concrete batching plants, for example, are generally used in areas not having hot water; much less energy supply lines. Such applications include concrete paving of remote areas and/or the building of concrete structures. Hot water boilers and/or other prior art hot water heating elements are of extremely limited use in such markets. While combustion fuel is, or may be plentiful, means for safely and efficiently utilizing combustible fuel to meet varying hot water supply demands is severely limited by prior art designs.
One difficulty encountered in combustion fuel hot water supply units of the prior art is the high carbon monoxide content in the end product. This difficulty is particularly prevalent in prior art fuel vaporizers. Such noxious vapor content is objectionable around human occupation; a generally occurring condition where hot water is needed. High carbon monoxide production is traceable to incomplete combustion, in the main, which is in turn traceable, in part, to difficulties in maintaining stable flames in most prior art vaporizing units. Excessive quenching of flames through direct radiative and convective contact between the flame and the feedwater is often the cause. The advantages that vapor generators might have in hot water supply systems have been overlooked in light of these problems and in view of the low pressure steam produced. To be effective, low pressure steam must be automatically convertible to high pressure hot water upon demand. Prior art boiler systems have not shown such capabilities and these hot water supply problems still exist. For this reason vapor generators have been developed for meeting such commercial and technological needs.
Vapor generators of the kind shown in U.S. Pat. No. 4,211,071 and in my copending U.S. patent application Ser. Nos. 37,029 filed May 8, 1979; 261,702 filed May 8, 1981; and 261,703 filed May 8, 1981, represent alternate means for supplying energy. The generators therein set forth material advantages over conventional boilers in the way of equipment simplification and reduced maintenance requirements. However, the product stream from a vapor generator contains a relatively high proportion of non-condensibles, which is undesirable in many applications. In the case of older forms of vapor generators, the non-condensibles include pollutants such as carbon monoxide and unburned hydrocarbons. In addition, when a high pressure stream is required, capital and operating costs for the air compressor stage of a vapor generator are high. It has also been observed that some energy consuming applications require a liquid product stream which is at a fairly high temperature and a very high pressure. Hot water flooding systems for recovering oil from reservoirs are one example. Other examples include the aforementioned heating of natural gas and petroleum pipelines.
The method and apparatus of the present invention address such hot water supply needs and overcome the problems of the prior art by providing a low pressure, vapor generator in which a demand sensitive product stream substantially free of carbon monoxide and other deleterious end use gases is produced. The vapor generator of the present invention may also be used in remote areas to produce a watersteam product at a sufficiently high heat energy state to convert large cold water supplies relatively quickly into a hot water at either low or high pressure.